Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for controlling Time Of Flight confidence map based depth noise.
Description of the Related Art
Time Of Flight based sensor measures a depth map by measuring a round trip time of pulse modulated LED light from a camera to the target object point. Usually, the depth map's coverage range corresponds to a half length of LED pulse.
As a result, a wrap-around error may occur. In other words, any object beyond the coverage range of Time Of Flight camera is mistreated as close to Time Of Flight sensor. Time Of Flight camera's depth calculation is based on the phase shift of light, which may be repeated for every a half length of LED modulation.
In addition, in Time Of Flight based depth map, the coverage range physically depends on LED modulation frequency. For example, 20 Mhz LED pulse modulation covers a depth range of 7.5 meter, 100 Mhz LED covers 1.5 meter depth range. Different coverage ranges are targeted depending on vision applications. Some vision application, such as, video conference requires 1.5 meters to 2 meter depth map coverage range. The higher is the LED pulse modulation frequency, the more expensive is the cost of TOF parts and the more difficult is having a stable LED pulse modulation status, even though higher LED pulse modulation allows more fine grained precision in depth map resolution.
Time Of Flight based sensor measures a depth map by measuring a round trip time of pulse modulated LED light from a camera to the target object point. Therefore, theoretically, the depth map's coverage range corresponds to a half length of LED pulse. However, the problem is an aliasing error. In other words, any object beyond the coverage range of Time Of Flight camera is mistreated rather as close to TOF sensor. It's because Time Of Flight camera's depth calculation is based on the phase shift of light. This problem is repeated for every a half length of LED modulation. Specifically, in an automobile vision application, Time Of Flight depth map aliasing error can generate significant vision system mal-function.
Therefore, there is a need for a method and/or apparatus for controlling Time Of Flight depth map.